Preparation of bituminous macadam



Patented Dec. 31, 1935 UNITED STATES PATENT OFFICE PREPARATION OF BITUMINOUS MACADAM Massachusetts No Drawing. Application July 28, 1931, Serial No. 553,700. In Great Britain July 30, 1930 1 Claim.

My invention relates to the manufacture of bituminous dispersions for binding mineral or fibrous aggregates to one another and to road surfaces, and to an improved method in which said bituminous dispersions are used for preparing bitumen macadam by a cold process, that is to say without applying heat to the aggregate of stone and/or to the bitumen.

The efficiency of bituminous dispersions for binding aggregates to road surfaces depends upon several factors such .as atmospheric conditions for example, temperature changes, the amount of water held by the aggregate and the texture of the stone.

I have found that the majority of bituminous dispersions which are used at present when applied to a road surface in the summer months of the year bind aggregate to it in a satisfactory manner, but that the same dispersions when used in cold wet weather possess little or no binding power.

An object of the present invention is to improve bituminous dispersions so that they will possess the power of binding aggregate such as chippings to a road surface under winter conditions and an enhanced binding power under summer conditions.

A further object of the present invention is to provide a bituminous dispersion from which a satisfactory bitumen macadam can be prepared by a cold process.

According to this invention the method of preparing improved bituminous dispersions consists in incorporating with a dispersion of bitumen a quantity of a liquid which is capable of softening the bitumen employed for making the dispersion and is miscible with the bitumen when incorporated with the dispersion. The liquid should not be too viscous and it has been found that one which does not readily spread also does not give satisfactory results.

Examples of suitable liquids serving the purposes of my invention are creosote, coal tar naphtha, shale oil, solar oil, petrol, kerosene, turpentine, Diesel oil, gas oil, fuel oil, those such as so-called Edeleanu extract and so-called Dubbs residue having a high aromatic content being particularly suitable.

Although the aforesaid liquids have various fluxing powers for softening bitumen, it has been found that in every case the incorporation of from about 5% to 20% of the liquid (calculated on the dispersion) is necessary to produce effective results. In general an incorporation of about 10% produces the most satisfactory results. It has been found that an incorporation of more than 10% of the liquid usually necessitates the use'of a harder bitumen in the dispersion, since the larger quantity of liquid tends to render the bitumen in the dispersion to fluid, with the result that a considerable time is required for the bitumen to harden satisfactorily when placed upon the road.

The following comparative experiments illustrate the advantage of the method of the present invention. 7

1. An aqueous bituminous dispersion containing approximately 51 per cent of bitumen was applied to a road surface and was chipped up with A, to /2 chippings. The result was so unfavourable that after three days every chipping had been swept off by traflic.

2. An aqueous bituminous dispersion as used in Experiment 1 but with 10% of creosote added thereto was applied on the same day and under exactly similar conditions and using similar chippings for covering. Perfectly satisfactory results were obtained, the chippings being firmly bound to the road surface.

The incorporation of the liquid with the bituminous dispersion is preferable effected by mixing into the aqueous bituminous dispersion the desired percentage of the liquid. If desired, however, the liquid may be mixed with the bitumen and the mixture then made into an aqueous dispersion. Alternatively the liquid may first be dispersed in known manner and the dispersion so obtained added to the aqueous bituminous dispersion, the proportions being adjusted so as to obtain the desired quality of liquid in the finished aqueous dispersion.

According to my invention I have found that a very satisfactory bitumen macadam is obtained by mixing an aggregate of graded pieces of mineral material which have a coating or covering of finelydivided calcium carbonate such as soft powdered limestone or chalk or dry hydrated lime with a bituminous dispersion of the kind as hereinbefore described which has an al kaline reaction. If crushed limestone is employed as the aggregate there is usually suflic ient powdered limestone clinging to the pieces to satisfy the purpose of this invention. Further soft powdered limestone or dry hydrated lime may, if desired, be mixed with the pieces of powdered limestone under stirring or agitation. If crushed slag, granite or basalt is employed as the aggregate the soft powdered limestone or dry hydrated lime is intimately mixed with the aggregate.

In an embodiment of the invention clean, air

dried, graded stone is placed in a mixer together with l%% its weight of hydrated lime, and thoroughly mixed for a period of one minute. If an eflicient mix has been obtained the lime should enter the surface voids and cling to the stone. A mixture consisting of 87.5 parts of bituminous dispersion of alkaline reaction containing approximately per .cent of bitumen of 200 penetration and 12.5 parts of creosote or other suitable solvent is then added to the extent of 5 to 6% by weight of the stone used and mixed in. As soon as the mixture has coated the stone the whole is discharged from the mixer. The coated stone leaving the mixer is a slatey brown colour, which after a period of five to ten minutes turns jet black with a considerable sheen.

The mixing can be effected in either a concrete or a so-called Tarmacadam mixer. If the concrete mixer is slow to give a uniform mix it is necessary to reduce the quantity of material loaded into the mixer, because if the material is left in the mixer for too long a period there is a tendency for the bitumen to be stripped from the stone and replaced by water before it is discharged from the mixer.

It is important to mix the ingredients, to remove the mixture from the mixer and to drain 01f the water in the mixture as quickly as possible.

The preparation of coated stone in accordance with my invention can be carried out at any central point or in the quarry since the material can be allowed to season like the socalled Tarmacadam and used at any time at will.

The prepared coated stone can for instance be laid in two coats consisting of a base coat made from 1% to 4" stone, and the top coat of uniform to V chippings.

The large stone for the base coat is usually coated with 8 gallons of the bituminous dispersion to the ton, and the chippings or small stone with about 12 gallons to the ton.

The method of laying the bitumen macadam prepared in accordance with my invention is exactly the same as that in existence for Tarmacadam, which is usually a 2 base coat and topping.

I claim:

A method of preparing bitumen macadam, which comprises mixing clean graded stone having less than 5% by weight of powdered limestone clinging to and substantially completely covering the surfaces thereof, with approximately 5% by Weight of an aqueous dispersion of bitumen, said dispersion containing approximately 50% of bitumen and 10 to 20% of a liquid capable of softening the dispersed bitumen, and continuing the mixing until the stone is completely coated with the dispersed bitumen.

AUGUSTUS G. TERREY. 

